Old Sunlight, New Map of the Sun's Magnetic Field in 3D

A team of US solar physicists has produced what it calls the first global, three-dimensional estimates of the magnetic field in the Sun's corona, the thin outer atmosphere that stretches beyond the visible edge of the disk. ^[1][2][3]

The magnetic field is the machinery behind solar flares and coronal mass ejections, the eruptions that can disturb satellites and power grids. It is also very hard to measure. The new maps are a demonstration of a method, applied to two dates, and not yet a way to forecast storms. ^[1][3][4]

Clues instead of a new instrument

The study appeared in The Astrophysical Journal Letters. It was led by Alin Razvan Paraschiv of the National Solar Observatory, with Zihao Yang and Daniela A. Lacatus of NSF NCAR, the US National Science Foundation's National Center for Atmospheric Research, and Momchil Emil Molnar of Southwest Research Institute. The authors' manuscript gives September 28, 2026 as the acceptance date. NCAR announced the findings on October 28. ^[2][3]

No new telescope was involved. The team worked from observations already collected at the Mauna Loa Solar Observatory in Hawaii, by the Coronal Multi-channel Polarimeter on October 14, 2016, and by its upgraded successor, UCoMP, on June 1, 2022. ^[1][2][3]

The data were already in hand. What is new is the way they are read. Paraschiv said the team is decoding light and waves that were already coming from the corona rather than depending on a new kind of instrument. ^[1][3]

How light and waves give up a field

The corona's magnetic field is difficult to measure directly, so the team combined two kinds of evidence instead.

The first is polarized light. Light from the corona carries a slight preference in the direction it vibrates, and that preference is shaped by the magnetic field it passed through.

Instruments record it as three quantities, known as Stokes I, Q and U. A fourth, Stokes V, is the one that is hard to measure in the corona, and this method does without it. ^[2][3]

The second is motion. Waves travel through the corona, and tracking them gives an estimate of the part of the field lying across the line of sight, which solar physicists call the plane-of-sky component. A plucked string works as a rough comparison: how it vibrates says something about how it is held. ^[2][3]

An inversion algorithm then works backward from both inputs to the field's direction and strength in three dimensions. The approach builds on the team's earlier global two-dimensional maps of the corona's field from UCoMP data, and on an inversion method called IQUD that had so far been tested only in theory and in statistical trials. ^[1][2][3]

The researchers describe the result as the first global full-vector inference of the coronal magnetic field from these kinds of observations. ^[2][3]

What the maps do not yet settle

The math does not give a single answer. For every pixel, the inversion returns four possible solutions, which differ in the signs of two components of the field. ^[2]

To draw a map, the team chose, pixel by pixel, the solution that agreed best with its neighbors. The authors say plainly that this is a qualitative choice made for visualization and does not resolve the ambiguity on physical grounds. ^[2]

So the pictures are a first look and not a finished measurement. The team says the method needs more development and validation before it can become routine. Lacatus said the initial results looked reasonable and comparable to what the researchers expected, and she invited other scientists to test and refine the approach. ^[1][3]

The invitation is real. The analysis software and the data sets are openly available. The method is not yet built into the data pipelines of any observatory. ^[1][3]

Not the same as the Inouye maps

The work should not be confused with another recent advance. In 2024 the Daniel K. Inouye Solar Telescope produced detailed maps of the strength of the coronal magnetic field using the Zeeman effect, a splitting of spectral light by magnetic fields. Those maps were a separate result. They measured field strength and did not infer the full three-dimensional field globally. ^[4]

The two lines of work come at the same gap from different sides.

Why it matters, and what comes next

The corona's magnetic fields shape its visible structures, and they are tied to the flares and mass ejections that reach Earth as space weather. A map of the field, rather than guesses at it, is the kind of input forecasters would want. ^[1][3][4]

That is a hope and not a result. Nobody has shown that these maps improve a forecast, and the team has demonstrated the method on only two days of observations. ^[1][3]

In principle, suitable CoMP or UCoMP observations could be used to generate maps for other dates. The researchers hope the method will eventually become a standard product of COSMO, a planned network of coronal observatories meant to follow the Mauna Loa facility. ^[1][3]

Tom Berger, director of the Mauna Loa Solar Observatory, said he was excited to see the data used to advance the ability to predict solar eruptions. He described COSMO as a way to fill an observational gap in the drivers of space weather. ^[1][3]

The next test is not a launch. It will come when a group outside the authors runs the open code on other days and sees whether the same fields come out.